Conventional practice involves removing rock debris created when boring a passageway through the subterranean strata without further reducing, albeit incidental reductions of the size of rock debris particles generated by a boring bit. Various boring bits, such as a polycrystalline diamond compact (PDC) bit, may produce a relatively high penetration rate by cutting larger particle size rock from the strata.
The time taken to conventionally bore a passageway is, generally, a balance between the rate of boring and the ability to maintain the pressure, suspension and velocity requirements placed on the circulating fluid slurry system and surface handling equipment used to remove rock debris from the subterranean passageway.
An aspect of the present invention includes increasing the removal rate of unused rock debris from a subterranean passageway by selectively placing rock breaking tools within a conduit string, that can be used to circulate fluid slurry, which can coat the bored strata wall and can remove the reduced particle size rock debris from the subterranean passageway.
The ability of the circulated fluid slurry to urge rock debris from the upper end of the passageway through subterranean strata, where it is processed by surface equipment, is, generally, dependent upon the ability to prevent significant losses of the circulated fluid slurry accompanied by associated losses of circulating pressure and velocity to subterranean fractures encountered or resulting from the rock boring process. The pressure integrity of the wall of the passageway through the subterranean passageway affects the ability of the fluid slurring circulating system to place pressure against the strata wall to increase velocity and to urge larger size rock debris from the upper end of the passageway.
Urging larger rock debris upward with circulated fluid slurry requires more pressure, velocity and fluid slurry suspension property, than urging smaller rock debris upward, because gravity and surface area have a greater effect on the larger particles. Larger particles often slip from the higher velocity centrally disposed fluid slurry stream, within an annular space, to the lower to zero velocity fluid slurry stream, immediately adjacent to an annular passageway walls, where rock debris may fall downward into cutting beds or re-enter the higher velocity fluid slurry stream for forming a slip stream pattern. It is very common to observe rounded edges at the surface when larger particles continually exit and re-enter the fluid slurry slip stream during the removal process.
Periodically, during boring and other well related operations, circulation can be stopped and the gel strength of the fluid slurry may be insufficient to keep larger rock debris particles suspended, resulting in larger particles falling downwards to form cuttings beds.
Reducing the particle size of rock debris increases the rate at which rock debris can be removed by reducing the slippage, relative to larger particles caught in slip stream patterns, or by forming cuttings beds when the fluid slurry has insufficient gel strength.
In deviated bore holes, the effect of gravity on rock debris often causes bored cutting beds to form on the lower side of the annular passageway, preventing the removal of rock debris over a large portion of the annulus. Additionally, if the gel strength of the fluid slurry is insufficient to suspend larger rock debris particles, they can fall downward and rest on inclined cuttings beds that may later shift downwards to trap drill strings.
Large rock debris falling downward and/or inventories or cuttings beds on the lower side of the annular passageway can represent serious risks to boring and other well operations within the passageway through subterranean strata. For example, conduit strings can become trapped or stuck within the bore hole by the accumulation of rock debris around the conduits.
An aspect of the present invention includes creating engagement and rock breaking apertures, that can be used to create a tortuous pathway within a fluid slurry circulated passageway to capture and break larger rock debris particles, while allowing smaller particles to pass. These apertures can be opened, closed, rotated and/or moved to increase the propensity to break larger rock debris more frequently, generating smaller, particle size rock debris sooner so that it can be more readily used or removed.
If the bored strata is prone to fracture, larger rock debris particles can act as proppants within a strata fracture, allowing pressure from the circulating system to reach the point of fracture propagation and potentially aggravating fluid slurry losses to the subterranean strata.
An aspect of the present invention includes reducing the particle size of rock debris, at the lower end of the subterranean passageway, so that the debris is less likely to act as a proppant within a strata fracture and can be more readily used as lost circulation material (LCM) to coat the strata wall and inhibit the initiation or propagation of fractures, which can threaten the pressure integrity of the strata wall and/or reduce the pressure and velocity available to urge unused rock debris from the upper end of the passageway through subterranean strata.
In another aspect, the present invention, can provide improved rock breaking characteristics of member embodiments selectively placed within a conduit string or a rock breaking tool deployed in a subterranean bore hole. This can be achieved by adapting members of the rock breaking tools to form apertures by, for example, open tooling passageway walls so that the rock debris can be impelled against the wall of the passageway through subterranean strata, thereby breaking rock debris and polishing the strata wall at the same time. Alternatively, adapted members using conduit gearing arrangements and/or fluid motors, with differing rotational speeds, can create opening and closing rock breaking apertures.
Another aspect of the present invention can involve additional internal passageways, that can be usable with any rock breaking tool, to drive radial disposed motors or to provide an axial rock crushing aperture with improved access to rock debris, through axial placement within a rock breaking tool.
Finally, another aspect of the present invention can include increasing the volume of reduced particle size debris, at the lower end of a bored passageway through subterranean strata. For example, immediately behind a boring bit generating rock debris, the volume of reduced particle size debris can be increased for immediate use or significantly improved removal, through the addition of adapted rock breaking tool members having higher torque and/or higher speeds using gearing and/or motor arrangements.
A need exists for reducing the particle size of rock debris at the lower end of the passageway through the subterranean strata to increase the immediately usable inventory of rock debris for inhibiting the initiation or propagation of strata fractures potentially threatening the pressure integrity of the fluid slurry circulating system.
A need exists to maintain the circulating system pressure integrity to ensure sufficient velocities are available for the efficient removal of rock debris from a passageway bore through subterranean strata.
A need exists for increasing the effective boring rate of penetration by improving the removal of rock debris from a strata borehole.
A need exists to reduce the risk of becoming stuck by falling rock debris and/or cutting beds on the lower side of an annular passageway.
Various aspects of the present invention address these needs.